Hi @cardtrixxer,
Are you using Cesium OSM buildings? If so, these buildings don’t come with textures. You can add some color to them by draping imagery over the tileset. This does not add textures to the sides, but can improve the visuals of the buildings from far away. There’s a walkthrough on this process here.
You can learn more about the Cesium OSM Buildings tileset here.
-Alex